1. Field of the Invention
The present disclosure relates to photo detecting devices, and more specifically to improvements for providing enhanced sensitivity to photo detecting devices and methods of enhancing the sensitivity of photo detecting devices.
2. Description of the Related Art
Photo detecting devices are found in everything from television remote controls to advanced weapon guidance systems. Photo detecting devices are generally defined as any radiant electromagnetic detecting apparatus. Examples may include photoresistors, photovoltaics, photodiodes, etc.
Electromagnetic radiation is classified by wavelength into radio, microwave, infrared, ultraviolet, X-rays and gamma rays. When light waves strike materials within certain photo detecting devices, a voltage and current are generated, or a change in electrical resistance will occur. As long as the light is present, the electrical voltage and current will modulate; and it stops when the light is removed. Any of the above conditions may be used to change the flow of electrical current or voltage in an external circuit and thus may be used to monitor the presence of the light and to measure the light's intensity.
The wavelength response of a photo detecting device shows a long-wavelength cutoff. If the wavelength is longer than the cutoff wavelength, the light energy is too small to produce a free electron and the response of the photo detector drops to zero. Photo detection device sensitivity to light pulses is generally developed during device fabrication, and there exists little means to improve sensitivity after fabrication. In some instances, electronic instrumentation is used to lower photo detecting device output noise. However, these instruments have low quality factors that reduce their ability to detect very low signals.
An electro-mechanical acoustic resonator is a mechanical device that will resonate when excited by a voltage in an electrical circuit. Some examples of electro-mechanical acoustic resonators include quartz crystal tuning forks, quartz crystal microbalances, microcantilevers and piezoelectric actuators. Quartz crystal tuning forks are typically used to keep extremely accurate time in quartz watches. The piezoelectric properties of quartz cause the quartz tuning fork to generate a pulsed electrical current as it resonates. Quartz crystal microbalances measure the change in frequency of a quartz crystal resonator and can be used to dampen oscillations. Microcantilevers work by measuring the change in deflection or vibrational frequency of the microcantilever. Piezoelectric actuators are transducers that convert electrical energy into a mechanical displacement or stress. The Piezoelectric effect is reversible, so an applied stress is capable of producing electrical energy in proportion to the stress on the material. The piezoelectric effect typically occurs in non conductive materials such as crystals and quartz.